The present invention relates to a suture anchor for securing a suture to a bone and, more particularly, to a suture anchor system configured so as to allow an axial seating force to be applied to an insertion tool engaged with a suture anchor, so as to seat the suture anchor within a bore in the bone, before the insertion tool can be separated from the suture anchor by the exertion of an axial separation force no less than the seating force.
Suture anchors are known in the art as providing a convenient and effective mechanism for securing bodily tissue to an adjacent bone structure in a human body such as, for example, where a ruptured tendon must be reattached to the corresponding bone. The suture anchor is generally inserted into a bore formed in the bone so as to provide an attachment point for securing a suture to the bone, wherein the suture is then used to secure the adjacent bodily tissue to the bone. Of the many types and forms of suture anchors, the wedge-type suture anchor has shown good promise in practical applications. Examples of such wedge-type suture anchors may be found in U.S. Pat. Nos. 5,540,718, 5,626,612, 5,782,863, 5,871,503, 5,879,372, 6,146,408, and 6,306,158 to Bartlett. U.S. Pat. No. 5,683,418 to Luscombe et al. and U.S. Pat. No. 5,961,538 to Pedlick et al., both assigned to Mitek Surgical Products, Inc., also disclose such wedge-type suture anchors. Thus, U.S. Pat. Nos. 5,540,718, 5,626,612, 5,782,863, 5,871,503, 5,879,372, 6,146,408, and 6,306,158 to Bartlett, U.S. Pat. No. 5,683,418 to Luscombe et al., and U.S. Pat. No. 5,961,538 to Pedlick et al. are incorporated in their entirety herein by reference.
Generally, in practice, a wedge-type anchor having an engaged suture is first engaged with an insertion tool and introduced into a bore drilled into the bone at a location on the bone where the bodily tissue must be affixed. The suture anchor generally includes a first gripping portion, such as a sharp edge or a point, and is designed to rotate as it enters the bore or is in the process of being withdrawn therefrom. As the suture anchor rotates, the first gripping portion bites or penetrates the wall of the bore and causes further rotation of the anchor. At the opposite end of the suture anchor, a second gripping portion is typically provided. The second gripping portion penetrates into the wall of the bore generally opposite the first gripping portion as the suture anchor is rotated, thereby wedging the suture anchor within the bore. When the suture anchor has rotated about the first gripping portion, as much as the second gripping portion will allow with respect to the bone structure surrounding the bore, the suture anchor is in a seated position where it is anchored in the bore and ready to have adjacent bodily tissue attached thereto.
However, while suture anchors are theoretically designed to work with all bones, the structure of bone can vary greatly depending on the area of the body in which the suture anchor is required. Bones generally include a number of trabeculae disposed throughout. The spacing of the trabeculae within the intermedulary canal of the bone is often a good indicator of the density of the bone. Cortical bone is solid bone without visible interstitial spaces and is typical of the midshafts, or diaphyseal regions, of long bones. Metaphyseal and epiphyseal bone, which is the bone around the joints at the opposing ends of the long bones, has a variable amount of cortical shells with a deeper trabecular structure, wherein the amount of cortical shells may vary greatly. Dense bone typically has small and closely spaced trabeculae, resulting in a hard and strong bone. In comparison, less dense or osteoporotic bone has larger and more widely spaced trabeculae, typically resulting in a softer and generally weaker bone. This less dense bone generally comprises a cancellous bone region about the intermedulary canal. A typical bone structure thus typically includes a cortical layer atop cancellous layer where the proportion of both types of bone may vary. Since the structure of bone may vary significantly from one area of the body to another, the specific performance characteristics required of a suture anchor also vary accordingly. Therefore, suture anchors must be able to function as intended when used in all types of bone structure. Where suture anchors are implanted into dense bone structures, well-defined strong gripping edges are required for the suture anchor to securely engage the bore in the bone. However, where the suture anchor is implanted into less dense bone, a large surface area engaging the bone is preferred in order to distribute and reduce the stresses on the relatively weak bone.
Several factors determine whether the implantation of a particular suture anchor will be effective. For example, wedge-type suture anchors generally depend on the rotation of the suture anchor within the bore in order to allow the gripping edges to interact with the wall of the bore to secure the suture anchor in place. Accordingly, the suture anchor must often be inserted into the bore in a particular orientation, which must be maintained in order to prevent the gripping edges of the suture anchor from engaging the wall of the bore until the suture anchor has been inserted to the proper depth. However, the suture anchor, once inserted to the desired depth in the bore, must then be properly seated by rotating the suture anchor such that the gripping edges engage the wall of the bore to optimally secure the suture anchor in the bone. Both of these factors should be considered in order to provide an effective suture anchor system.
The Luscombe et al. '418 patent and the Pedlick et al. '538 patent each disclose wedge-type suture anchors which are angularly shaped, generally approximating a triangle to a quadrilateral and having straight sides. According to one aspect of these references, an insertion tool is used for implanting the suture anchor in the bore, wherein the insertion tool is configured to have a frangible portion at or near the interface of the insertion tool and the suture anchor. The frangible portion is further configured to break or separate from the suture anchor after implantation thereof in the bore. However, the frangible portion of the insertion tool may limit the orientation at which the suture anchor may be introduced to and inserted into the bore without fracturing the frangible portion. Such limited mobility may also cause the gripping edges of the suture anchor to engage the wall of the bore before the proper implantation depth has been attained. Accordingly, the limited mobility of the insertion tool having a frangible portion may not facilitate rotation of the suture anchor and may render it difficult to attain a seated position for the suture anchor before breakage of the frangible portion. Where a seated position has not been attained, a tensile force on the suture engaged with the suture anchor may undesirably be required in addition to or in the alternative to a tensile force on the insertion tool.
The application of a tensile force on the suture to seat the suture anchor may not be desirable for several reasons. For example, since the seating force for the suture anchor is applied by an individual, it would be very difficult to achieve the desired seating force, much less a consistent seating force, between applications. In addition, the location of the bore in the suture anchor through which the suture is looped may not be appropriately located on the suture anchor to allow a tensile force on the suture to provide any rotational force for seating the suture anchor. As such, the suture anchor may not be properly seated if the seating force is insufficient and the suture anchor may thus not provide the necessary securing force for securing the adjacent tissue to the bone. Alternatively, the suture may be broken or pulled out of the suture bore, or the suture anchor broken or pulled out of the bore, if the seating force is exceeded. Accordingly, in these instances, the implantation procedure may have to be performed again and at a different site, using a new suture anchor. Still further, it may also be difficult to design and manufacture a suture anchor having the necessary mechanical properties for implantation according to this procedure.
In the alternative, Luscombe et al. '418 patent, the Pedlick et al. '538 patent, and the Bartlett '718, '612, '863, '503, '372, '408, and '158 patents each describe a discrete flexible metallic insertion tool comprised of, for example, a shape memory material, which engages a bore in the anchor in a friction fit. Such flexible insertion tools may be beneficial in maintaining the suture anchor in a desired orientation upon insertion thereof into the bore, as well as for facilitating the manipulation or rotation of the suture anchor toward a seated position. However, since the insertion tool is only engaged with the suture anchor via a friction fit and thus may be easily separated therefrom, a tensile force directly on the suture engaged with the suture anchor may be required in order for the suture anchor to attain a seated position. Alternatively, the suture may be held against or secured to the insertion tool to maintain the insertion tool in engagement with the suture anchor such that the necessary tensile force can then be applied on the insertion tool to seat the suture anchor. Accordingly, in either instance, the tensile seating force is undesirably applied to the suture anchor via the suture.
Still further, the Pedlick et al. '538 patent describes a threaded connection between the suture anchor and a flexible insertion tool. However, such threaded components may be difficult and time-consuming to form on both the suture anchor and the insertion tool. Further, the suture anchor may undesirably rotate about the axis of the insertion tool during the suture anchor seating process, thus making it difficult to rotate the suture anchor toward the seated position within the bore. In addition, it may also be very difficult to appropriately configure the threads to attain and consistently control the seating force which may be applied on the suture anchor and/or the necessary force for separating the insertion tool from the suture anchor. In some instances, a seating force applied on the insertion tool may strip the threads in the suture anchor or cause other damage thereto. If, in these instances, the suture anchor is not properly seated, the stripped threads would prohibit the insertion tool from being re-engaged with the suture anchor so as to further apply a seating force and thus the undesirable application of the seating force directly to the suture may be the only remaining option.
Thus, there exists a need for a suture anchor system having the desirable suture anchor implantation characteristics of a flexible insertion tool comprised of a shape memory material, while allowing a predetermined seating force to be applied on the suture anchor before the insertion tool is removed from the suture anchor following insertion thereof in the bore. Such a system would desirably provide predetermined and consistent seating characteristics of the suture anchor in the bone.